Textbook Question
Write a short essay that discusses sex chromosomes as they contrast with autosomes.
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Ch. 7 - Sex Determination and Sex Chromosomes
Klug12th EditionConcepts of Genetics ISBN: 9780135564776
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Table of contents
- Ch. 1 - Introduction to Genetics17
- Ch. 2 - Mitosis and Meiosis36
- Ch. 3 - Mendelian Genetics51
- Ch. 4 - Extensions of Mendelian Genetics74
- Ch. 5 - Chromosome Mapping in Eukaryotes51
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages46
- Ch. 7 - Sex Determination and Sex Chromosomes33
- Ch. 8 - Chromosome Mutations: Variation in Number and Arrangement40
- Ch. 9 - Extranuclear Inheritance31
- Ch. 10 - DNA Structure and Analysis43
- Ch. 11 - DNA Replication and Recombination44
- Ch. 12 - DNA Organization in Chromosomes30
- Ch. 13 - The Genetic Code and Transcription54
- Ch. 14 - Translation and Proteins47
- Ch. 15 - Gene Mutation, DNA Repair, and Transposition41
- Ch. 16 - Regulation of Gene Expression in Bacteria29
- Ch. 17 - Transcriptional Regulation in Eukaryotes41
- Ch. 18 - Post-transcriptional Regulation in Eukaryotes33
- Ch. 19 - Epigenetics33
- Ch. 20 - Recombinant DNA Technology44
- Ch. 21 - Genomic Analysis36
- Ch. 22 - Applications of Genetic Engineering and Biotechnology36
- Ch. 23 - Developmental Genetics37
- Ch. 24 - Cancer Genetics34
- Ch. 25 - Quantitative Genetics and Multifactorial Traits54
- Ch. 26 - Population and Evolutionary Genetics45
Chapter 7, Problem 5
Describe the major difference between sex determination in Drosophila and in humans.
Verified step by step guidance1
Understand that sex determination is the biological system that determines the development of sexual characteristics in an organism.
Recognize that in humans, sex determination is primarily based on the presence or absence of the Y chromosome: individuals with XY chromosomes develop as males, and those with XX chromosomes develop as females.
Note that in Drosophila (fruit flies), sex determination depends on the ratio of X chromosomes to sets of autosomes (non-sex chromosomes), rather than the presence of a Y chromosome.
Specifically, in Drosophila, a ratio of X chromosomes to autosome sets of 1.0 (e.g., 2X:2 sets of autosomes) results in a female, while a ratio of 0.5 (e.g., 1X:2 sets of autosomes) results in a male.
Summarize that the major difference is that humans use a chromosomal system based on the presence of the Y chromosome for sex determination, whereas Drosophila use the X chromosome to autosome ratio to determine sex.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sex Determination in Drosophila
In Drosophila, sex is determined by the ratio of X chromosomes to sets of autosomes (X:A ratio). A ratio of 1.0 (e.g., XX) results in a female, while a ratio of 0.5 (e.g., XY) results in a male, regardless of the presence of a Y chromosome.
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Sex Determination
Sex Determination in Humans
Human sex determination depends on the presence or absence of the Y chromosome. Individuals with an XY chromosome pair develop as males due to the SRY gene on the Y chromosome, while XX individuals develop as females.
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Role of Chromosomes vs. Chromosome Ratios
The key difference lies in the mechanism: Drosophila uses the X-to-autosome ratio to determine sex, making the Y chromosome non-essential for maleness, whereas humans rely on the presence of the Y chromosome and its genes to trigger male development.
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Related Practice
Textbook Question
How do mammals, including humans, solve the 'dosage problem' caused by the presence of an X and Y chromosome in one sex and two X chromosomes in the other sex?
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Textbook Question
What specific observations (evidence) support the conclusions about sex determination in Drosophila and humans?
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Textbook Question
Distinguish between the concepts of sexual differentiation and sex determination.
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Textbook Question
Contrast the XX/XY and XX/X0 modes of sex determination.
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Textbook Question
The phenotype of an early-stage human embryo is considered sexually indifferent. Explain why this is so even though the embryo's genotypic sex is already fixed.
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